I'd recommend buying an external firewire800 (or usb2.0) enclosure and buying a nice, big, silent, and cool hard drive to put in it. Then sync the two with any of the available freeware/shareware on the internet to do the job.
Currently I just backup to another drive in the same system.
I just have an xcopy job that runs every morning at 3am.
Eventually I'll want to move to an external drive.